The present invention relates to a capacitive position sensor, particularly an angular position sensor for determining the position of a throttle valve in an internal combustion engine.
In many fields of technology it is required to determine the position of an element of a device in order to influence certain operational variables or parameters of the device in dependency on the ascertained position.
In the motor vehicle technology it is necessary, among other things, to determine the position of the throttle valve and to transmit corresponding information to a control apparatus for adjusting predetermined operational parameters, such as ignition time points, injection duration and the like, of the internal combustion engine.
It is known to ascertain the throttle valve position by means of a potentiometer. Due to wear phenomena, this solution has the disadvantage of an insufficient reliability. In particular, during operation of an internal combustion engine, very large temperature fluctuations and strong vibrations occur. Consequently, resistance potentiometers in the long run cannot guarantee sufficient reliability under such operational conditions.
From the U.S. Pat. No. 4,644,570 an inductive position pickup device is known. It includes coils arranged on a substrate and cooperating with movable elements in the form of circular segments whose relative position to the coils is ascertained by means of eddy current measurement. The coil arrangement is mirror symmetrical and the more a circular segment overlaps one coil the more it clears the other coil. The coils are connected to an electronic evaluation circuit. However, the discrete current paths in the respective coils of the arrangement produce corresponding ripples in the magnetic fields through which non-linearities result.